Stripe along center of mirrored model?
That line you see when you use the mirror modifier is there because the UV maps do not coincide with the image used as texture. If you look close the edges are right where the transparency starts or there is a different tone of yellow.
Move the edges of the UVs inside the solid color or add additional color to the image.


Also, you have a set of unnecessary faces at the seam of the mirror modifier. Get rid of them.